Expert Working Groups

EUFAR ICCP Cloud Expert Workshop

The EUFAR ICCP Workshop on Data Processing, Analysis and Presentation Software of Cloud Probes took place at the University of Manchester from 23 to 24 July 2016. More than 40 cloud measurement experts and students from Europe, America, Asia and Australia participated in the workshop with the objectives to summarise current data processing algorithms for measurements made with cloud spectrometers operated on research aircraft, to discuss differences in the data processing methods, to assess optimum practices and to recommend a way forward in improving data quality from cloud probes.

After a welcome and introduction to the workshop by Darrel Baumgardner (Droplet Measurement Technologies), Christiane Voigt (leader of EUFAR’s expert working group on In Situ Characterisation of Cloud and Precipitation Particles) presented an overview of EUFAR activities. Colin Gurganas (SPEC) showed a new study that addressed the oversizing of out-of-focus particles by the 2D-S. The session continued with a discussion of open issues related to cloud data processing. Darrel Baumgardner presented a summary of results from a questionnaire on data processing issues that had been responded to by 15 participants. The summary included current practices on data corrections for airspeed, out of focus particles, shattering and ice crystal size/habit definition. Greg McFarquhar (University of Illinois) showed a study that underscored the uncertainties in deriving particle size distributions, using the same data set from optical array probes (OAP) but processed by three separate groups. Although the same algorithms were supposed to be implemented in the processing, there were significant differences that still remained due to different criteria for accepting particles.

The next session introduced eight different software packages to process and display measurements from cloud probes. These were developed and are maintained by the University of North Dakota (David Delene), University of Manchester (Jonathan Crosier), University of Illinois (Greg McFarquhar/Wu Wei), NCAR (Aaron Bansemer), previous standards & protocols engineer under EUFAR 2008-2013 (Matt Freer), SPEC (Colin Gurganas) and Environment Canada (Alexei Korolev). The day ended with an introduction and a tutorial to Python by Nick Guy and Matt Freer.

A discussion on the way forward in cloud data analysis was opened on day two. This included a dialogue on definitions of microphysical cloud parameters and corrections to be applied to cloud data analysis. The urgent need for a common international reference library that includes the individual processing algorithms was agreed upon by the 43 participants in attendance. The reference database should be a living document with a quality control by referencing to existing literature or by an internal review process and an easy follow up of track changes. The possibility to assign a DOI for individual processing algorithms was emphasised. Simulated or experimentally derived data sets can serve as reference cases to test, evaluate or compare the processing algorisms. EUFAR, who currently maintains EGADS (EUFAR Airborne Data-processing Software), was recommended as a possible first choice to host such a database. In addition, an intercomparison paper on cloud data processing algorithms is planned as one outcome of the workshop. These actions will be initiated by Darrel Baumgardner, David Delene and the international cloud community possibly in connection to the EUFAR expert working group on cloud instrumentation. The progress can be followed in workshops linked to the ICARE2 international conference on aviation research hosted by EUFAR in 2017 and the AMS/ICCP conferences in 2018 and 2020.

In summary, the workshop offered a unique opportunity to bring together leading experts and young scientists to exchange information in the challenging and fast evolving field of airborne cloud measurements. The action items that were identified in this workshop and that will be carried out in the near future will be an important step forward in the interaction within and outside of the cloud physics community to improve the quality and fidelity of cloud measurements.